Interferometric lithography is a maturing technology for patterning large area, periodic sub-micron features. The interference of two or more coherent optical waves is recorded in photoresist to produce a variety of structures including gratings, holes, posts, cones, and grids. This lithographic technique allows maskless patterning of large area substrates using short exposure times. Applications for periodic patterns include distributed feedback lasers, field emission displays, liquid crystal displays, advanced data storage applications, optical gratings, metrology standards, and sub-wavelength structures. Our work is motivated by interest in bringing interferometric patterning out of research laboratories and into mainstream production facilities for high volume applications, by automating and simplifying the exposure process. The concept and operational principles of two automated interference lithography systems, the HLS model 1000, and the HLS model PC2, are introduced.